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Friday December 23, 2011 2:34 pm

AMD Radeon HD 7970 review


AMD Radeon 7970

The perpetual war for supremacy between AMD and Nvidia constantly leaves enthusiasts dodging shrapnel: When you want the best video card you can afford, why buy one now instead of waiting for the better one the competing chipset designer will undoubtedly release in a few months? This leaves reviewers in a tough spot, too, as we're constantly proclaiming that nearly every new card is the fastest ever. But because you can only live in the world you live in, we're obliged to go there. So, here goes once again: The just-released AMD Radeon HD 7970 ($549 list) is the latest fastest and most feature-rich single-GPU card ever, surpassing our previous Editors' Choice winner, the Nvidia GeForce GTX 580.

Though we have little doubt that Nvidia will yank back that title with its next generation of cards, the 7970 is an impressive achievement for the moment.  (It's rumored to become widely available by early January of 2012.)  The inaugural member of the Southern Islands family, it utilizes a fresh architecture AMD refers to as "Graphics Core Next." Based on a new 28nm process technology and utilizing more than 4.3 billion transistors, Graphics Core Next uses a revised instruction set architecture, gives each compute unit the ability to simultaneously execute instructions from multiple kernels, and delivers an increased number of instructions per clock cycle per square millimeter of GPU space. The result, so AMD claims, is "designed for high utilization, high throughput, and multitasking."


We'll examine how well the 7970 achieves those goals in due time, but first we should look more deeply at what the card offers on a component level. The maxed-out new Southern Islands GPU (the 7900 series, code-named "Tahiti") can contain up to 32 compute units (CUs) supported by two geometry engines and rasterizers (one of each for every collection of 16 CUs), one L2 cache up to 768KB, four render back-ends (offering 32 color ROPs per clock and 128 Z/stencil ROPs per clock), and a 384-bit GDDR5 memory interface with bandwidth up to 264GBps. Cards in the 7900 series can also make full use of the newest and speediest PCI Express (PCIe) 3.0 x16 bus interface.

AMD didn't stop with just internal developments. The company promises that the Southern Islands cards will offer improved cooling and acoustics, by way of a new sixth-generation vapor chamber and a wider fan with new blades that are capable of wicking away more heat than before. Power issues have received plenty of attention as well, with PowerTune technology for intelligent monitoring of energy usage on an application-by-application basis when the proper electrical and thermal headroom are available.

Also new is ZeroCore Power Technology, which shuts down the GPU and turns off the fan during long idle states, for a reduction in idle power usage of up to 95 percent. According to AMD, this delivers additional benefits in CrossFireX configurations: Secondary GPUs are always in the ZeroCore Power state when they're not in use, with the primary GPU joining them during long idle periods, thus saving even more power in systems that traditionally suck it up with party-animal abandon.

Like all of the company's video cards, those in the 7900 series support DirectX 11 (and it's posed for DX11.1 when Windows 8 comes around) the full range of AMD's proprietary technologies. Eyefinity is back, but with a twist: Though it still makes for an easy way to run multiple monitors, the 7970 is the first card capable of driving three stereoscopic 3D displays by itself using new monitors that support DisplayPort 3D; the 7900 series isn't even limited to a single audio stream, but can out multiple independent streams at once. Other new Eyefinity features introduced with the Catalyst 11.10 driver update include new monitor configurations (5-by-1 landscape and portrait), full support for setups using multiple 1,920-by-1,200 and 2,560-by-1,600 monitors, and flexible bezel compensation.

If the 7970 sounds beefy from a spec standpoint, it is indeed. The card's 250-watt TDP hasn't changed from the 6970, but almost everything else has been dialed up. The card is driven by an astonishing 2,048 stream processors and has a 925MHz engine clock; AMD estimates the card delivers 3.79 teraflops of compute performance. Thirty-two ROPs and 128 Z/stencils max out the GPU's capability. Memory has been packed on, too, with the 7970 housing a remarkable 3GB of GDDR5, twice what the GTX 580 carries; the bandwidth is the aforementioned 264GBps, the memory clock runs at 1,375MHz, and the overall data rate is 5.5Gbps. (The last two specs are not increases over those of AMD's last-generation top single-GPU card, the Radeon HD 6970, for what it's worth.)

Video outputs are a strong collection as well, with two Mini DisplayPort jacks (supporting the DisplayPort 1.2 standard), one HDMI 1.4a port, and one dual-link DVI port. The last is beginning to look mighty legacy, as both the Mini DisplayPort and HDMI ports are now capable of driving the 4K displays that are almost certainly coming in the next generation or so. (AMD touts its cards as being the first on the market to support this new hardware.) And there is again a switch that lets you return to the factory settings any time you want, so you can overclock to your heart's content safe in the knowledge it will be tough to do any permanent damage.

Positive as all this is, the typical downsides to such a powerful card are here as well.  You will need to run two additional cables from your power supply (one eight-pin, one six-pin), and the card's oversize fan–heat sink unit means it blocks an adjacent expansion slot. But because the card is of a reasonable length (11 inches), these are minor annoyances well in keeping with video cards this high up in the enthusiast spectrum.

What does all this mean in terms of gaming performance? A lot. In our testing (on a system set up using an Asus P9X79 Deluxe motherboard running the Intel Core i7-3960X CPU) we saw some significant jumps over both AMD's own 6970 and Nvidia's GTX 580. The 7970's overall 3DMark 11 score was 2,734, an 861-point increase over what we saw from the 6970 (1,873) and 619 points higher than what the GTX 580 earned (2,115). The 7970 triumphed in almost all of our gaming benchmarks, often by large degrees, at least at 1,920 by 1,200. When we tested Aliens vs. Predator at that resolution, for example, the 7970's result of 55.1 frames per second (fps) was well ahead of the 6970's 47.2fps and the GTX 580's 43.6fps. The 7970 barely eked out a playable 31fps against the GTX 580's 27.2fps in Total War: Shogun 2 at 1,920 by 1,200, though the GTX 580 couldn't even run the game's benchmark with all the details cranked.

The 7970, it should be noted, didn't ace every test. The GTX 580 did marginally better in DiRT 3 (69.5fps versus 66.9fps) and HAWX 2 (140 versus 130), both at 1,920 by 1200. And a lot of the 7970's impressive leads dropped at 2,560 by 1,600, with only about 7fps separating the cards at Aliens vs. Predator (34.7fps versus 27.5fps), 1fps at DiRT 3 (47.7fps versus 46.7fps, the 7970 winning the competition here it couldn't quite at 1,920 by 1,200), and 12fps in Just Cause 2 (40.6fps versus 28.6fps, as compared with the wider gap between 60fps and 36.8fps for that game we saw at 1,920 by 1,200). And looked at beside either AMD's or Nvidia's more expensive dual-GPU gaming cards, the Radeon HD 6990 and the GeForce GTX 590 respectively, the 7970 looks like small performance potatoes. (Though, for the record, the GTX 590 couldn't run Total War: Shogun 2 at 2,560 by 1,600.)

Where the 7970 really distinguished itself was in terms of power usage. AMD's efforts in this regard really paid off, as our test bed was able to idle at an impressive minimum of 99.8 watts; that's less than we saw with either the 6970 (107.8) or the GTX 580 (117.3). But when running under full graphics load the 7970's full-system power draw rose to only 245.9 watts—again, this is below the results we got from both the 6970 (249.8 watts) and the GTX 580 (264.6 watts), and the 7970 gives you the most polygon-pushing power.

So, folks, it's that time again to declare a new Editors' Choice and a new "sensibly priced" (as opposed to the dual-GPU models, anyway) enthusiast video card. No matter what game you want to play or, within reason, what resolution you want to play it at, this is the one-GPU card that will excel most at the job best. Its price may still be steep, and you may be able to find GTX 580 cards on the market for less (around $500), but if full-tilt gaming without compromises is what you crave, you won't be able to do better than the AMD Radeon HD 7970. At least for a while.

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